Many optical system assemblies have strict requirements for optical performance such as high transmission, low pupil non-uniformity, low RMS wavefront errors, and low transmitted wavefront asymmetries. Design and tolerance considerations play important roles in meeting wavefront performance requirements. For example, design forms are often chosen to reduce sensitivity to expected types of optical aberrations (wavefront errors) accompanying the manufacture of optical elements, and tolerances of the optical elements are chosen with respect to the design sensitivities so that manufacturing variations do not severely influence the system level performance. Nevertheless, during the optical assembly even properly designed and manufactured optical elements, when stacked together can introduce additional wavefront errors that degrade overall performance of an optical assembly.
For optical systems where polarized light is used for imaging or illumination, the transmission characteristics of the optical elements usually drive material, design, and tolerancing choices for the optical system assemblies. For example, optical materials may be chosen for their index of refraction and optical transmission properties to meet basic imaging requirements.